Photographically useful agents that are previously incorporated in a photographic light-sensitive material such that their effects will be produced at the appropriate time contain various features different from those which are used as an addition to a processing solution. Specific examples of the features in the former case are as follows: The incorporation in a photographic light-sensitive material enables effective utilization of photographic agents of the kind which tend to decompose under the acid-alkaline or the oxidation-reduction condition, and consequently, can not withstand long-time storage, in a processing bath. At the same time, such makes it possible to simplify the composition of the processing solution to be employed therewith and thereby to facilitate the preparation of the processing solution. Further, this makes it possible to force a required photographic agent to function in desired time during the photographic processing or at only the desired place, that is, in only a specified layer and the neighboring layers of a multilayer photographic light-sensitive material. Furthermore, this permits the presence of a photographic agent in the photographic light-sensitive material in such an amount as to vary as the function of silver halide development. However, if a photographic agent is added to a photographic light-sensitive material in its active form, it becomes impossible to make the photographic agent exhibit its ability to the expected degree because during storage before photographic processing, it reacts with other components contained in the photographic light-sensitive material or it is decomposed by heat, oxygen or so on.
One method for solving the above-described problem involves adding a photographic agent to a a photographic light-sensitive material in such a form that its active group is blocked and turned photographically inactive, that is, in the form of its precursor. Such a method can have various advantages in various cases to which it is applicable. For instance, in the case where the useful photographic agent is a dye, blocking a functional group of the dye which has a great effect on its spectral adsorption characteristic results in a shift of its spectral absorption band to shorter wavelengths or to longer wavelengths and therefore, even if the dye is present in a silver halide emulsion layer having the spectral sensitivity in the wavelength region corresponding to the absorption band which the dye has in the unblocked state, a lowering of the sensitivity due to the so-called filter effect can be prevented.
In another case where the useful photographic agent is an anti-foggant or a development restrainer, blocking of their active groups makes it possible to suppress desensitization arising from adsorption of these agents to light-sensitive silver halide grains and formation of silver salts upon storage. At the same time, release of these agents at required times permits the reduction of fog density without being attended by decrease in the sensitivity, the prevention of fog due to overdevelopment, development stoppage at a desired time, and so on.
In still another case where the useful photograpic agent is a developing agent, an auxiliary developing agent or a fogging agent, if their active or adsorptive groups are blocked, various photographically adverse effects which arise from semiquinones and oxidants produced by air oxidation upon storage can be prevented. Generation of fogging nuclei upon storage can also be prevented because injection of electrons into the silver halide grains can be inhibited. Therefore, stable processings can be effected therein.
In a further case that the useful photographic agent is a bleach accelerating agent or a bleach-fix accelerating agent, it also becomes possible to prevent reactions, with other components copresent in the photographic light-sensitive material, from occuring upon storage by blocking its active group and that, to make its expected ability bring into full play at a desired time by removing the blocking group.
In the present invention the above-described active group, functional group and adsorptive group are generally referred to as active group.
As described above, a precursor of photographic agents can be utilized as an extremely valuable tool in bringing out the abilities of the photographic agents to the best advantage. However, their precursor must satisfy very severe requirements for practical use. That is, the precursor must satisfy two requirements contradictory to each other; one is ensuring stable presence of the precursor under a storage condition, and the other is setting its blocking group loose at a desired time upon the processing and releasing the photographic agent rapidly and efficiently.
A number of techniques for blocking a photographic agent have already been known. For instance, a technique using a blocking group such as an acyl group, a sulfonyl group or the like is described in Japanese Patent Publication No. 44805/72 (corresponding to U.S. Pat. No. 3,615,617): one which utilizes such a blocking groups as to release a photographic agent by the so-called reversal Michel's reaction is described in Japanese Patent Publication Nos. 39727/79 (corresponding to U.S. Pat. No. 3,674,478), 9696/80 (corresponding to U.S. Pat. No. 3,791,830) and 34927/80 (corresponding to U.S. Pat. No. 4,009,029): one which utilizes such a blocking group as to release a photographic agent with the production of quinone methide or its analogs by intramolecular electron transfer is described in Japanese Patent Publication No. 39727/79, Japanese Patent Application (OPI) Nos. 135944/82, 135945/82 and 136640/82: one which utilizes an intramolecular ring-closing reaction is described in Japanese Patent Application (OPI) No. 53330/80: one which utilizes cleavage of a 5-membered or 6-membered ring is described in Japanese Patent Application (OPI) Nos. 76541/82 (corresponding to U.S. Pat. No. 4,335,200), 135949/82 and 179842/82: and so on. However, these photographic agents blocked with known blocking groups suffer from the defect that, for example, although stable under a storage condition, some precursors require a high alkaline condition, such as a pH higher than 12, for processing because the photographic agent-releasing rate thereof is too slow; some precursors decompose gradually to cause a failure of their function as the precursor under a storage condition, even though it can release the photographic agent at a sufficiently fast rate by processing under mild conditions such as in a pH range of 9 to 11; some precursors allow little latitude in controlling the rate of releasing the photographic agent therefrom and therefore, it requires a very narrow pH range for effecting the processing; and so on.